Limit bandwidth for pure-ftpd

I want to limit the total FTP bandwidth to 4 meg on each of my ISPConfig servers so that all users on that server share that 4 meg. Googling seems to indicate there is not a parameter that you can put into /etc/pure-ftpd/conf like you can when setting passive port ranges. It appears that you have to call a parameter -t or -T when starting up pure-ftpd. Where is that located? the command for pure-ftpd so I can add that option at startup time?